The general purpose of this invention is to improve the spatial and spectral resolution performance characteristics of glancing incidence X-ray telescope systems capable of broadband, high-resolution imaging of solar and stellar X-ray and XUV (extreme ultraviolet radiation) sources. For certain applications, such as with very high resolution X-ray detectors coupled to extremely high spatial resolution primary mirror systems, very large magnifications may be of great value. Super high-resolution imaging with the most advanced X-ray telescope systems currently being planned for launch in the 1990's on NASA's space station program indicate the desire for coupling systems capable of providing very high magnifications to the initial image; possibly even as high as 10.times. to 40.times..
Instruments such as the Advanced X-ray Astrophysical Facility (AXAF) are designed with the greatest emphasis upon the harder rather than the softer components of the X-ray spectrum. The requirements of high magnification, coupled with the short distance typically afforded by instrument envelope constraints, essentially rule out the possibility of the utilization of large magnification glancing incidence hyperboloid/ellipsoid X-ray microscope optics such as are currently being developed as a part of the NASA Extended Range X-ray Telescope Program.
Furthermore, systems such as have been disclosed in applicant's copending application Ser. No. 571,613, filed on Jan. 17, 1984, entitled SPECTRAL SLICING X-RAY TELESCOPE WITH VARIABLE MAGNIFICATION are not ideally suitable for this application, as normal incidence LSM (layered synthetic microstructure) optics cannot be utilized at wavelengths significantly below 30 angstroms or so.
In the prior art, the Wolter X-ray telescope system is typically used to focus the X-rays from a point source (or an extended source) at infinity to a high-resolution image on the sensitive surface of the detector situated at the prime focus of the Wolter system. For soft X-rays (wavelengths ranging from 2.ANG. to 100.ANG.) the Wolter type I mirror system with coaxial and confocal, concave paraboloidal and hyperboloidal elements (both of which are internally reflecting) is typically used. Such telescopes were flown on the Skylab space station and have been used on the Einstein and Copernicus observatories in space.
High-resolution imagery has been achieved by use of high-resolution detectors, such as photographic emulsions directly in the prime focus of the Wolter X-ray telescope; or with a high-resolution solid state detector placed in the focal plane of a long focal length telescope. Photographic emulsions limit the spectral coverage of X-ray telescopes due to the absorption of soft X-ray and XUV radiation in the gelatin and, consequently, these detectors have relatively low effective quantum efficiencies. The solid state detectors limit the performance, from a spatial resolution point of view, due to the large size of the image elements.
Techniques for coupling Wolter telescopes to solid state detectors by means of convex hyperboloid mirror systems have been described in the above referenced copending application of applicants entitled SPECTRAL SLICING X-RAY TELESCOPE WITH VARIABLE MAGNIFICATION.
The primary disadvantages of utilizing the telescope directly with the detector is that the full resolution capabilities of the primary X-ray mirror system are not utilized.
Furthermore, these methods provide little or no spectral information. Thin metal foils have been mounted on a rotating filter wheel to obtain crude filtergrams of solar X-ray emissions. Due to the nature of these filters, the bandpass is of necessity very broad, which is a great detriment to detailed analysis and plasma diagnostics. Higher spectral resolution can be achieved by means of an objective grating placed immediately behind the Wolter telescope optics. However, for a multipurpose instrument, great care must be taken to ensure that the grating can always be removed from the optical path and that failsafe mechanisms are employed. However, the concave ellipsoidal LSM optics that constitute the novel components of this disclosure can intercept all of the divergent beams from a complex nested system. These optics are easy to construct, even if it is desirable for the magnification to be in the range of 20.times. to 50.times., which we believe will be desirable for certain high-resolution applications.
Accordingly, an important object of the present invention is to provide a glancing incidence X-ray telescope system capable of broadband, high-resolution imaging of solar and stellar X-ray and extreme ultraviolet radiation sources.
Another important object of the present invention is to provide an X-ray telescope system which can be utilized over a broad band of X-ray and extreme ultraviolet radiation sources in the range of thirty angstroms and below.